Trigger circuit



J. G. KREER, JR

TRIGGER CIRCUIT Oct. 14, 1952 Filed May 26, 1950 CURRENT FIG. 5

CURRENT lNVENTOR J G. KREE/BL/r ATTORNEY Patented Oct. 14, 1952 TRIGGER CIRCUIT John G. .Kreer, Jr., Bloomfield, N.0J., assignor to Bell Telephone Laboratories, Incorporated, New York, .N. Y., a corporation of New .York

Application May 26, 1950,SerialN0. 164,361

'17 Claims.

This invention relates to signal translation systems using negative-resistance units as the active elements.

It is the general object of the invention to provide new and novel electric circuits of the type designated as trigger or double-stability circuits.

It is also -an object of this invention to utilize small two-terminal negative-resistance units of the inert or passive type to produce a trigger circuit having two conditions of equilibrium.

It 'is notable of the double-stability circuits of this invention that they are capable of being repetitively triggered or changed from one to the other of their two conditions of equilibrium by successive impulses of the same polarity.

It is also a feature of the invention that "two small inert or passive type negative-resistance units are utilized in double-stabilitycircuit arrangements which require a minimum-o'f space and power requirements for the production of suitably shaped discontinuous wave forms, such asirectangularly shaped waves.

'The subject invention is characterized by its use of two current-conduction paths or circuit -meshes in which electric currents flow continuously but in unequal amounts. Each of these paths includes a variableresistance unit that'has a region of negative resistance over a portion of its variational characteristic, which region is flanked byztwo adjacent regions of positive resistance. The circuit parameters areso'chosen that neither variable resistance unit will operate 'in itsregion of negative resistance; but one unit will operate in its positive-resistanceregion on one-flank f thenegative-resistance region while the other unit operates initsipositiveresistance :region on the other flankof the negative-resistance region. An energy storage or memory circuit interconnects these two fcircuit meshes "or.conductingzpathsand stores energy ilraccordancevwith the diiierence in the'values of .theicurrentszflowing in the variable units. If a momentary circuit disturbance causes the current in "each path to be changed to such .a degree that both variable resistance units-are simultaneously operated'in their region ofipositive resistance on the same :fiank oi the negative-resistanceregion,

,thereris an unequal change inthecurrents fiow- .ing 'inthe two branches and a consequent: redistribution of the stored energy. At the terminationof the momentary'disurbance the totalcurrent flow 'in the two branches is. restored itodits prev-iousvalue butthe division1.of'current between the branches is reversed Thatiis, the highecurrentpa'thbecomes the low-current'pathlandvice the opposite sense or polarity to the original stored energy. This revised current-conduction condition-is a stable one andwillbemaintained until a subsequenticircuit disturbance in the .form of a triggering'impulse causes the circuit'to revert tolits original condition. Arrangements are made for extracting suitably shapedirelated voltagelimpulses.

The manner in which the invention "accomplishes the above-mentioned objects will bemore clearly apprehended from a'con'sideration-oi :the following descriptions of 'a few preferred-embodiments thereof, when consideredin conjunction with th'e' drawings, in which:

Fig. 1 is a schematic 'circuit arrangement of one embodiment of the inventionin which'seriestype negative-resistance elements are employed in the current-conduction paths, in which the sourceof reversing pulses is connectedvbetween the par allel conduction paths;

Figs. 2 and Gare current-voltage and voltagecurrent characteristics, respectively,to which references are made'in the following descriptions;

.Fig. 3 is a schematic of a second embodiment of 1a double-stability circuit in accordance with the invention using series-type negative-resistance elements in which the source of :reversing pulses is serially connected with the parallel .cionduction paths;

Fig. 4 tea schematic c'ircuit'of a double-stability circuit in accordance with the invention in which theznegative-resistance elements are of the specific type'known as transistors,and in which 'asingle energy storage unit is employed; and

5 is a double-stability circuit arrangedJin accordance with :the invention in which shunt- "ty'peinegativeeresistance elements are utilized The variable resistance units that are utilized in this invention are'well known in the art and may take a'var'iety of forms. Although this invention is primarily concerned with the use of small inert or passive type negative-resistance units because of their extremely small size and low power requirements, it will 'be understood thatitmay'be practiced equally well through-the useioI" ionic or electronic discharge devices, or for that :matter with are discharges. In'the-fol lowing descriptions the invention'will beset'forth interms of .twoimain classifications of negativeresistance units, rather with reference to a specific unit. However, there will be describedone tested embodiment of :the invention in which small flake-type thermistors were utilized. these units will be more completely identified in connection with the description of Fig. 1.

Negative-resistance units have been generally classified as seriesor shunt-type units, and will be so referred to herein. The series type of unit is often referred to as an open-circuit stable or current-controlled unit. A graph of its currentvoltage characteristic is an N-shaped curve which shows a region of negative resistance in which an increase in the current flowing through the unit is accompanied by a, decrease in the voltage drop across it. This region is flanked on the left and right by regions of positive resistance in which an increase in current flow is accompanied by an increase in voltage drop across the unit. Thus, for a given value of voltage drop across the unit there may be as many as three appropriate values of current. If this type of unit is serially connected to a positive resistance the value of which is at all times greater than the maximum value of the negative resistance, the unit is stable, hence its classification as an open-circuit stable unit. If the connected resistor is less than this maximum negative value the unit is unstable and the current flowing through it will never come to rest at a value corresponding to the negative-resistance region but will quickly traverse this region and come to rest in the positive-resistance region to the left or right of the negative region. These left and right regions of positive resistance will be referred to herein as the first and second regions, respectively.

The shunt type of unit is said to be voltagecontrolled or short-circuit stable. A plot of the values of current flowing in the unit for various values of voltage impressed across the unit has the general shape of an 8 curve. This curve shows a region of negative resistance that is flanked on the bottom and top by regions of positive resistance; which regions may be referred to herein as the first and second positive-resistance regions, respectively. This shunt type of unit is in nearly all respects the converse of the series type of unit. Thus, in the region of negative resistance an increase in the impressed voltage is accompanied by a decrease in the current flowing through the unit, and for a given value of current flow there may be as many as three values of voltage across the unit. If this type of unit is connected in parallel with a positive resistance which is at all times less than the minimum value of the variable resistance in its negative region, the unit is stable. If so connected with a resistor of value greater than this minimum value, the unit is unstable, and the voltage across the unit will never come to rest in the negative-resistance region; but will quickly traverse this region to rest in its first or second region of positive resistance depending upon whether the disturbance is an addition or reduction in magnitude of the impressed voltage.

In Fig. 1 there is shown the circuit arrangement of a double-stability or trigger circuit in accordance with the invention in which the variable or negative-resistance units are of the seriesor current-controlled type. Therefore, in order to utilize the unstable characteristic of these units, each is connected in series with a padding resistor the magnitude of which is less than the maximum value of the variable unit in its negative portion of its variational characteristic.

In this tested arrangement, the negativeresistance units I4, [6 which are here shown as variable resistors in a broken line rectangle, were a species of the general class of variable resistors that has been named varistor, and specifically is called a thermistor because of its property of changing its resistance in accordance with changes in its temperature. The tested units were substantially identical flake-type or thinfilm type thermistors similar to those described in Patent 2,414,793, January 28, 1947, to J. A. Becker. They could equally well have been beadtype thermistors, point-type rectifiers such as the germanium crystal diode; or, as will be explained in connection with Fig. 4, they could be the more recently publicized semiconductor arrangement that has come to be known as transistor.

Each of resistance units l4, It has a variational resistance characteristic of the type indicated by the current-voltage graph 30 of Fig. 2. Current source or battery l0 together with current-limiting series resistor l 2 is connected across the parallel current-conducting paths comprising variable resistors l4, I6 and their connected padding resistors i8, 20. A pair of capacitors 22, 24 are connected in series between the junctions of the fixed and variable resistance units; and a pulse generator 28 is connected between the junction of resistors I8, 20 and the junction of capacitors 22, 24. Generator 28 is connected so that its pulses as they pass through variable resistors 14 and I6 are in opposed polarity to the current from source 10. Output terminals designated Out are connected across padding resistor 20.

The general principles governing the choice of suitable values for current source or battery I0, limiting resistor l2 and padding resistors i8, 20 Will be explained with reference to the currentvoltage characteristic curves of Fig. 2. Referring to that figure, curve or graph 30 indicates the manner in which the voltage across a series-type or current-controlled negative-resistance unit changes as the current flowing through the unit is varied. This curve is representative of the general class of series-type units and is not individual to any specific unit. It is indicative of the variation that would be noted if a thin-film resistor composed of one or more of the oxides of manganese, nickel, cobalt or other suitable metal, such as is described by Becker in the previously referred to Patent 2,414,793, were connected in series with a source of variable unidirectional current and a large-valued stabilizing resistor. The variation in voltage or voltage drop across the thermistor would be similar to that shown on curve 30 if the current flowing in the resistor were varied.

From this curve it will be noted that the unit has a region 38 to 40 of negative resistance in which an increase of current produces a corresponding decrease in voltage across the unit. This region of negative resistance i flanked on the left by a first region of positive resistance extending from zero to reference numeral 38, and is flanked on the right by a second region of positive resistance to the right of reference numeral 40. These first and second regions are occasionally referred to as the low-current and highcurrent regions of positive resistance, respectively. There is only one appropriate value of voltage or voltage drop for any specific value of current flowing through the device, but, for any given value of voltage drop there may be as many as three appropriate values of current flow in the unit. The curve portion between reference numerals 38, 40 1 a region in which a change in the current flowing through the device produces an oppositely directed change in the voltage acrossthe device. This, therefore, is a region of instability and is not one in which the current how will come to rest unless the unit is in series connection with a stabilizing resistor of sulficiently great value. If the stabilizing resistor is greater than the maximum negative resistance of the negative-resistance unit, any current value may be stably maintained. This maximum negative resistance occurs at a current corresponding to the point 52 at which. curve has its maximum negative slope.

The constant slope curve it (Fig. 2) indicates the potential drop across one of the padding resistors l8, 2%] as the current through the resistor is increased. The combined current-voltage characteristic of a serially connected series-type negative-resistance element 14, I6 and its associated padding resistors i8, 20 is shown by curve of Fig. 2. It will be noted from this curve that the negative resistance region, as indicated by curve portion 38', id is constricted from that for the negative-resistance unit alone, as indicated by the curve portion 38', of curve 30. This compression of the negative-resistance region is caused by the addition of the padding resistor, and is a function of the magnitude of this resistor. If the associated padding resistor is less than the above-described maximum negative resistance, the curve 32 will include such a region as indicated by the numerals 38', Mi. Any change in current that brings the operation within the curve portions 38', 4G promotes the regenerative action that is inherent in the device and causes the current to quickly traverse this region of negative resistance and to come to rest at an appropriate value in its first, low-current or second, high-current region of positive resistance. It this characteristic of the negativeresistance element that is employed useful purpose in the subject invention.

It may be seen that the padding resistor should not be of such valu that the negative-resistance portion of curve 32 is completely eliminated. In actual practice, the padding resistor should be sufficiently below this limiting'value to allow a suitably large or extended negative-resistance region, as seen on the current-voltage characteristic curve of the negative-resistance element, to permit the desired trigger action. One consideration to be borne in mind is that increased stabilwith respect to extraneous voltage impulses may be expected to accompany extended negative-resistance range.

An analogous situation exists in the shunt-type voltage-controlled or short-circuit stable unitiin which the current varies as the voltage across the unit is varied. This characteristic of the shunttype unit will be later discussed withrelation to Fig. 6. It is mentioned at this time in order to emphasize that each'type of unitihas a negative" resistance region of instability for electrical quantities within a predetermined or specified range of values.

Current source or be. ing resistor l2 may be a rather wide range of value will to a large extent dete. e the magnitude or the pulse from source that provides the desired trigger action. Ingeneral, for a given operating condition, a reduction in the potential of mitacross the combined resistors.

positive voltage regions.

tially from each other.

also reduce the required magnitude of. the reversing pulses from source-=23. Current source In and resistor H are chosen of such values that when connected in series with the parallel conducting paths including negative-resistance units 14 and i8, the'total current flowing'through resister lZilies between the values of twice the current value corresponding to the voltage maximum 38' across the combined resistors and twice the current value at the voltage minimum 40 From an inspection of curve 32 it will be seen that, when the total current in the circuit is maintained between thcsetwo limiting values, negative-resistance units. M, It may not both be simultaneously operating .in their high-current or low-current Therefore, one of these negative-resistance units must necessarily operate in itslow-current positive resistance region to the leftof point33' at the same time that the other is operating in its high-current pcsitiveresistance region to the right of point All.

Capacitors 22 andzdimay be suitably chosen of equal value. They'are preferably of such size that a substantialfraction ofthe potential difference that exists across these units at the beginning of the reversing pulse from source 28 continues'to existiacross them at the end of the pulse period. Themaintenance of this potential differential is desirable in order that the current conduction state of each negative-resistance unit M- and IE will be reversed after each pulse interval.

Pulse source 28 is'of sufiicient magnitude and is so poled that it momentarily reduces (to a value less than. the minimum value 49) the voltage across negative-resistance unit M or i6, whichever is conducting high current. The pulse from source 28 is preferably of duration that is a substantial fraction of the time required for the negative resistance units l4 and Ill to reverse their current-conductionstates. Therefore, the duration of this pulse may be increased when slow-speed units are used and decreased when high-speed units are used.

In one tested embodiment of the invention, suitable values for the designated components were as follows:

Battery H) 60 volts Current-limitin resistor I2 10,000 ohms Capacitors 20, 24 r. 3,000 microfarads Resistors I8, 20 3,300 ohms Pulse source 28 33 volts Negative-resistance units l4, l6 were flake-type thermistor units composed of nickel, manganese, and cobalt oxides such as are described in the pre viously mentioned J. A. Becker Patent 2,414,793. Their thickness was such that they had a time constant of about milliseconds or less and a current-voltage characteristic such that a maximum'voltage (point 38, curve 30) of about 18 volts coincided with a current voltage or" about .18 milliampere and a minimum voltage (point 48) of about L5 volts corresponded to a current value of 10 milliamperes.

Although in the above-described. embodiment the values of components in the two current-conduction paths have been shown to be substantially similar, modifications of this circuit are conceivable in which the characteristics of the two negative-resistance units i4, i6 and the values of their series-connected resistors I8, 28 diifer substan- This also applies to the circuits to be described hereinafter.

It is interesting to note that had the potential of source 10, in this tested embodiment of the invention, been reduced to about 25 volts and the magnitude of the resistor I2 had been reduced to about 1,500 ohms, a magnitude of only 8 or 9 volts would be required for the pulses from source 28 to insure reversal of the double-stability unit.

The manner in which the double-stability unit of Fig. 1 operates to alternately change from maximum current conduction to minimum current conduction in each path may be best apprehended if an initial set of current conditions is assumed. For this purpose, assume that the total current from battery It! is limited to the sum of the two values corresponding to points 34' and 35' on curve 32 and that the negative resistance M and padding resistor 18 initially constitute the maximum current-conduction path. Under these conditions, the current flowing in negative-resistance unit 16 is less than that in unit H, but the voltage across unit I6 is greater than the voltage across unit I 4. The voltage drop across padding resistor 18 exceeds the drop across resistor 20, and capacitors 22, 25 are charged with the negative terminal connected to resistor it. If source 28 now supplies a voltage impulse between the common terminal of resistors I8, 25 and the common terminal of capacitors 22, 24 the polarity of which with respect to the common terminal of resistors I8, 20 is the same as the polarity of source 10, the voltage across negative-resistance unit M is changed to a value less than its voltage minimum 4!] (curve 39, Fig. 2). Referring to this curve, it will be noted that when the voltage across the negative-resistance unit is reduced below the voltage minimum value 40, the unit is brought within its range of instability. The current in the unit cannot rest between reference points 38 and 43 (curve 33) so it quickly traverses this region to rest at a value in the low-current positive-resistance region corresponding to the new voltage value 45 (curve 36). During the period just preceding the pulse interval in question, negative-resistance unit 58 was operating at point 34 in its low-current positive-resistance range. and the voltage across it was greater than that across unit I l. Upon the application of the voltage pulse from source 28, the voltage across this unit is lowered by the same amount as that across unit I4; however, because it was initially operarp ing in its low-current positive-resistance range, its current conduction is only slightly lowered and remains at a higher value than the revised value for unit I4 (represented by point 45). Capacitor 22 discharges through resistor I8 and temporarily maintains the voltage across resistance unit I at a lesser value than that across l6. At the termination of the pulse, the full potential of source I0 again becomes effective to increase the current flowing in both units. Because the voltage across unit is is now greater than that across unit I and this difference tends to be maintained by the discharge of capacitor 22 as the currents through the negative-resistance units I 4 and I6 simultaneously increase, it is apparent that unit 16 will reach its point of voltage maximum (point 38) before unit M reaches this point. Therefore, as the current continues to increase, unit 16 is forced through its negative resistance region (Mtill) and into conduction in its high-current positiveresistance region to the right of point 40 (curve 30). This action results in a sudden increase in the total current flowing in the circuit, which increase is limited by the voltage drop across ourrent-limiting resistor 52 in such fashion that the total current in the circuit is again maintained at a value that is less than twice the current flowing in either negative-resistance unit at its point 40 of voltage minimum. Hence, the current conduction through unit I4 is limited to its low-current stage. During the interval of the reversing pulse from source 28 and immediately following the cessation of this pulse, the potential difference across capacitors 22 and 24 is redistributed, that is, capacitor 22 discharges and capacitor 24 charges in such fashion that the potential difference that previously existed between these units is maintained in magnitude but is reversed in direction by the now larger current flow through padding resistor 20. Thus, a half cycle of operation is completed, and the main current carrying path is changed from resistance unit [4 to resistance unit Hi. In addition to acting as a padding resistor, resistor 20 also functions as a load resistor. At the time of each change in the magnitude of the current flowing through negative-resistance unit [6, there is a corresponding change in the potential drop across resistor 20, which change is available at the output terminals designated Out in the form of a rectangularly shaped voltage wave. These current-conduction conditions are maintained until the next succeeding impulse from source 28 causes unit 16 to revert to its lowcurrent positive voltage region of operation and unit M to change to its high-current positive voltage condition in the manner which has been previously described.

As described in the foregoing pulse source 28 is poled in a direction to reduce the potential across the variable-resistance current-conduction paths. However, it will be apparent from a study of curves and 82 of Fig. 2. that the circuit of Fig. 1 could also be operated with the polarity of pulse source 28 reversed, the added pulses being of suflicient magnitude to enable both variable-resistance units to operate on the upper positive portions of the current-voltage characteristic for the duration of the pulse.

Fig. 3 shows the schematic arrangement of a slightly different embodiment of the invention in which the source 28 of reversing voltage impulses is connected between one terminal of the current source or battery l0 and the common junction of padding resistors 18, 20 instead of in the manner shown in Fig. 1. As in the arrangement of Fig. 1, the polarity of the voltage pulses from source 28 are chosen to be in opposition to the polarity of battery i=3. Therefore, the required polarity with respect to the common junction of resistors 18, 2D is reversed from that of Fig. 1. Under certain operating conditions, this may be found to be a convenient form of the invention; such as, where certain grounding arrangements must be ob served. In addition to the foregoing consideration, the arrangement of Fig. 2 also differs from that of Fig. 1 in that the impedance termination of source 28 is slightly different in the two arrangements. In most instances, this will not be a material consideration.

Fig. 4 shows a schematic arrangement of a third embodiment of the invention in which each negative-resistance unit 46, 50, comprises a semiconductor triode of the type which has become commonly known as a transistor; and which is described and claimed in Patent 2,524,035 of John Bardeen and W. H. Brattain, issued October 3, 1950. Each of these units comprises a small block of semiconductor material, such as N-type germanium, with which are associated three electrodes. One of these, known as the base elecparagraphs, the

stantially exceeds unity for electrode current voltage conditions within. a. preassigned range of values. When such a semi'conductor-triode is connected, as shown in Fig.4, the points 38 and 4!) (curve 33, Fig. 2) ofvoltage maximum and minimum are-functions of the magnitude of the shuntin resistor 48 or 52. Thus, changes in the magnitude of'thisresistor permit placing the points 38 and 40 of voltage maximum and minimum at the desired values. Thesenegative-resistance transistor circuits areseriallyconnected withpad-ding resistors f8 andto form parallel conduction paths across which are connected a third circuit branch made up of" current source or battery ill,current-limiting;resistor l2, and'a source of voltage impulses 28; As in the previously described embodiments, pulse source 28 is poled in such manner thatits pulsesopposite in polarity the potential"of"battery"IU: Gapacitor lid i connectedbetweenthedunction' point 56* of transistor 46" and, resistor l8 andjunction point,

53 of transistor 50 andresistor 2B. Transistor units 4% and 50', when arranged as; shown, constitute series-type negativeeresistance units having a representative current-voltage character: istic, as shown by curve 300i Fig. 2. The same considerations control the choiceof' magnitudes for battery It], current-limiting resistor l2, and padding resistors l8 and 20', aswas described in connection with the circuit.arrangementof Fig.1..

As was previously explained, by limiting the total current flow in the ci'rcuittoa value which. lies.

between the two limiting] values of, less than twice the current corresponding. to the. voltage minimum 46 across the combined negativeresistance and padding resistor and more than twice the current corresponding to the voltage maximum 38 across these units, thestable current-conduction states in the. two parallel circuit branches comprising the transistors; 46,. 50 are unequal. If it is assumed that transistor 46; is

at a given instant, conducting: a-yhigh-current.

value, transistor 50 will be conducting a lowcurrent value, and the potential drop across padding resistor 13 will exceed that. acrossresistor Capacitor 54' will have a positive potential charge on its-plate adjacent to point 56. It now a reversing voltage impulse is applied from source so as to reduce the potential across transistor til to a value less than its; minimum value 40, capacitor 54 will drive circulating current aroun the loop made up of capacitor; 54 and resistors 58 and 20 in such arway'as, to tend to'maintain the potential difference between reference points lit? and 58. Hence, the current through transistor- Et will be greater than that through transistor 56, and if the pulse is, removed beforecondenser it: is discharged, transistor 50 will transfer to the high-current state. Capacitor 54 will then discharge and recharge in the; reverse direction in, which its terminal .adi acent.-,iunction. 5831s 10 positive. At the same time of the next reversing voltage impulse from source 26, the. same cycleof events takes place, but in the reverse direction, and transistor 46 is returned to the high-current state, while transistor 50 returns to the low current state, thus completing a full cycle 01:"

operation. Simultaneously, currents flowing in resistor 20 produce changed potential. drops acrossresistor 2B which are available at the output. terminals designated, Out in the form of rectangular voltage impulses.

In. Fig.- 4 the output is shown as connected acrosspadding resistor 20. It is equally possible to conne'cttheoutput across either resistor 48' or'52;

Fig. 5 iswaschematic of a circuit inaccordance with the inventionin which the negative-resistanceunits-GU, 5'4 are shunt-type negativeresistance elements. Each of these elements 60, 64 may have a current-voltage characteristic such' as isshown bythe representative curve 14 of Fig. 6 This characteristic is. distinguished by the fact that as the voltage across the negative-resistance unit is increased. from zero, the current through the unit first increases until it reaches a maximum. value indicated at reference point 15. A further increase of the voltage across this unit causesthecurrent to decreaseuntil itreaches a minimum valueatpoint 18, after which further increase. of'voltage causes increased current. It is thus seen that each of these elements possesses a region of. negative resistance between reference pointslfi and 1.8 which is. enclosed by a first or low-voltage region or positive resistance and a second or-high.-vo1tage region of positive resistance. Theseunits are distinguishable from those described in connection with Fig. 1 in that there is only one related value of current corresponding to each value of voltage across the unit; whereas there maybe as many as three values of related voltage across the unit for a single value of current.

This characteristic is the reverseofthe seriestype characteristic exemplified by curve 30. of Fig. 2. These shunt-type negative-resistance.elements: 60;, 64' areconnected in series with potential source or battery [0, voltage dropping resistor l2, and pulse source 28-, as indicated. Resistors 62; 68 are connected in series and are shunted across the negative-resistance units. An inductor fill is connected between junction point 1030i the-negative-resistance units and junction point 1'2 of resistors-52,66.

The considerations governing the choice of Y magnitudes for the various components of the arrangement of Pig 5 are similar to those that have been described in connection with theiarrangement of Fig, l. Resistors 62, 66. are preferably equal, or nearly equal. Each; may be chosen from a wide range of values subjecttothe limir tation that itshall not be less than" the minimum negative resistance of the shunt-type element (approximatelyindicated at point 536, curve M) so that the current-voltage characteristic of the combination of one of these resistors-in-parallel with its associated negative-resistance-unit 50' or 64 has a negative slope or-negative-resis ance portion, as is: shown by the maxi-mum: and minimum current reference points 32, The. potential of battery l0. and the resistance at 1 esistor l 2-are chosen so that the potential difference across the serially connected negative resistance units 653, 6 shall always ee-greaterthan twice. the voltage across the com ination of one of, these units and its paralleled-jfixed; re-

sistor at the point 82 of current maximum and less than twice the voltage across the combination at point 84 of current minimum.

When the values of battery I and currentlimiting resistor l2 are chosen to produce a voltage condition within these limits, there will be a total current T (Fig. 5) flowing in the circuit. This current T corresponds to three possible voltage conditions across the negative-resistance units. One condition (point 85, curve 14) corresponds to the high-voltage operating condition of the negative-resistance unit. A second condition (point 88) corresponds to the low-voltage operating condition of the negative-resistance unit. The third condition falls within the negative voltage range of the negative-resistance unit. Since this is a region of instability, it will not come to rest in this condition. Under these conditions, there will not be a stable rest state in which the voltage across one negative-resistance unit is equal to that across the other unit. Analogous to the series-type arrangement, one of these shunt-type negative-resistance units will operate in its high-voltage positive-resistance region at point 85 on curve 14, while the other is operating in its low-voltage region at point 88 on this curve. The sum of the currents through negative-resistance unit 60 and its shunt resistor 62 will always equal the sum of the currents through negative resistance -54 and its shunt resistance 66.

The manner of operation of this arrangement is similar to that which has been previously described for the series-type negative-resistance units. Assume an initial condition in which negative resistance 60 is operating at point 85 in its high-voltage state and negative resistance 64 is operating at point 88 in its low-voltage state. A relatively high value of current will fiow through negative resistance 64 and resistor 62, and a relatively low value of current will flow through negative resistance 60 and resistor 66. The difierence between these two values of current fiows through inductor 68. Because of the energy that is stored in the magnetic field around inductor 68, the current conduction through inductor 68 cannot change instantaneously. Therefore, if an impulse is supplied from source 28, the currents flowing through negative-resistance units 60 and 64 will also be reduced in such manner that the difierence between the currents fiowing through these units remains substantially unchanged. This current reduction reduces the current through negative resistance 60 to a value less than its current minimum 18, and this unit reverts to its low-voltage operating condition at point 90 in which the current through it is less than that through negative-resistance unit 64. At the termination of the pulse from source 28, the current through negative resistances 69, 64 starts to increase uniformly, and negative resistance 64 reaches its current maximum condition I6 and is forced through the negative-resistance portion of its characteristic before unit 60 reaches its current maximum condition. Resistance unit 64, therefore, transfers to its high-voltage lowcurrent state (point 85, curve 14), and unit 60 is maintained in its low-voltage high-current state at point 88 on this curve. Current fiow through inductor 68 decreases to zero and then builds up to a stable value in the reversed direction consistent with the revised current conditions. At a later instant when a second current pulse is supplied from source 28, the previously described redistribution of potentials with its consequent change in current flow is performed in the reverse direction, thus restoring the circuit to its initial condition and completing a full cycle of operation. At the time of each potential change, there is a revision in the current flowing through padding resistor 66 which also serves as an output load resistor. These revised current conditions produce square wave voltage impulses which are available at the output terminals designated Out.

It is evident from the preceding description that the subject invention may be practiced through the use of a variety of circuit arrangements, a few preferred ones of which have been described herein. It should be appreciated that there exist several suitable negative-resistance units, either of the seriesor shunt-type, which may be used with equal facility to those that have been described herein in carrying out this invention. In view of this, it is to be expected that variations of the invention which do not depart from its spirit and scope will present themselves to those skilled in the related art.

What is claimed is:

1. A double-stability trigger circuit which comprises a pair of variable resistance elements each of which possesses a negative resistance over a restricted portion of its current-voltage range having a minimum and a maximum voltage value, a pair of fixed resistance elements each connected in series with a respective one of said variable elements to form a pair of branches, a capacitive circuit connected between the common points of said respective variable and fixed resistance elements, a source of potential, currentlimiting means connecting said source across both of said series-connected resistance branches and effective to limit the current from said source to a value less than the sum of the currents corresponding to said minimum voltage values and greater than the sum of the currents corresponding to saidmaximum voltage values, and means for momentarily reducing the current in said branches to a value less than the sum correspondingto said maximum voltage values comprising a source of unidirectional voltage impulses connected intermediate said source of potential and said variable resistance elements.

2. A double-stability trigger circuit which comprises a pair of variable impedance elements each of which possesses a negative impedance over a restricted portion of its current-voltage range having a minimum and a maximum voltage value, a pair of fixed impedance elements each connected in series with a respective one of said variable impedance elements to form a pair of impedance branches, energy storage means interconnecting said respective variable and fixed impedance elements, a source of potential connected-across both series-connected impedance branches, said source being limited to a current less than the sum of the currents corresponding to said minimum voltage values, and greater than the sum of the currents corresponding to said maximum voltage values, and means for momentarily reducing the current flow through said impedance branches to a total value less than a predetermined minimum value.

3. An electrical trigger circuit comprising a pair of variable resistance elements and a pair of connected fixed resistors forming therewith a pair of current-conduction paths, each of said variable resistance elements in combination with each said fixed resistor having a variational resistance characteristic which is represented by a first region in which one stable operating state obtains exclusively for a given set of conditions,

and a second region in which another stable operating state obtains exclusivelyfor agiven set of conditions, and a region intermediate said first region and said second region in which either of said stable operating states obtains for agiven set of conditions, an: impedance element connectedto each of said elementszand forming therewith a current conductionpath, an external network interconnecting said current conduction paths,,said: network including a source of energy the magnitude of which issuch that both of said elementsare operated in said intermediate region simultaneously, whereby each of said elements stabilizes in a different one of'said stable operating'states', said network includinga source of. unidirectional, electric pulses, and energy storage means coupling said current-conduction paths to store energy, in accordance-with the difference in said current-voltage operating conditions of said variable resistance elements, said stored energy effecting an interchange of the, operating conditions in said elementsat the; termination of each pulsefrom said source.

4; An electrical trigger circuit comprising pair of negative-resistance elements each of which is-characterized bya variational resistance characteristic which is represented by a first region in which a first stable operating state obtains exclusively for" a. given operating condition,, a second region in which a second stable operating state obtains exclusively for-a given operating condition, and a region intermediate said firstand said second regions in which either of said firstor said second stable states obtains for a given operating condition, a. fixed resistance connected to each of said elements and forming therewith a current-conduction path, an external network interconnecting said currentconduction paths, said network including a unidirectional source of electrical energy of such a magnitude as to operate each of said elements in said intermediate region simultaneously, whereby each of said elements stabilizes in a different one of saidoperating states, said networkalso including arsource of unidirectional electricalpulses for changing the effective value ofsaid'electrical source to give ris'e'to a conditionof the system in which each of said elements is in the same stable operating state, and energy storage means interconnecting said conducting branches.

5. An electrical doubleestability" circuit com-- prising a pair of variable resistance units, a pair offixed resistance units each of which is connected to a respective one of said variable units, each of said connectedcombinations being, characterized by a variational resistance characteristic having'a predetermined range of electrical quantities within'which either of-two stable rest states obtains for a given set of conditionsand' outside of which only a' single stable rest, state obtains for a given set'of conditions, asource of continuous unidirectional energy interconnecting said connected resistance units, the energy'of' said so urcelimited in magnitude to values within said predetermined range of electrical quantities for both or said elements; wherebyeach of said elementsstabilizes in a different one of said stable'rest states, asource of unidirectional voltage pulses'connected between said energy source and said variable resistance units thev magnitude of said pulses being sufficient to changeduring their duration the effective value of"saidunidirectional energy source toa value which gives rise to operation; outside of said predetermined range for bothbf'said elements simultaneously whereby: each: of' said elements is momentarily in the same stable operating state, and a reactance element interconnectin the junctions of said fixed and variableresistance units.

An electrical double-stability. circuitcomprising a pair of variablerresistance units anda respective fixed resistance unit connectedto each, each of said. connectedvariable and fixed units having a current-voltage characteristic that: is characterized by'a first region inwhichone stable operating condition obtains exclusively. for any given condition, a second regioninzwhichqam other" stable operating state? obtains exclusively for any given condition;: and an intermediate region between said first: and said second .regions'. in whicheither one'ior'ithe other of said stable operating conditionspbtains for-any given condition, an external: network: interconnecting said combined units, said network including .a source of continuous unidirectional; energy the magnitude of which is equaltd twice the value required to producefin one of said combinations the current-voltage conditions corresponding gto said intermediate region and a.source, ofrunidirectional energy impulses the. polaritiesof which are opposed tothe polarity ofzsaid continuous energy source, t1ie magnitude of said. impulses being sufficient to:momentarily bring, both re sistance combinations within, thecurrent voltage conditionscorresponding to one of said regions outside. said intermediate region, and reactive member coupling: said." fixed and variable resistance combinations 7. An electrical doubleestability circuitcomprisinga pair of variable resistanceaunits and a pair of respective .fixedresistanceunits: connected thereto, each of said variable resistance units and its respective connected fixed resistance units having a current-voltage characteristic that is characterized by a first. region in which one stable operating staterobtains, a'second region in which another stable operatingstateobtains, and a region intermediate, between said first and second regions'in,whicheither. one: or, the other of said stable operating states obtains, an external network interconnecting said connected resistances, said network including a source of continuousunidirectional energy, said source of continuous energyhaving a: value sufiicient to produce current-voltage conditions corresponding to said intermediate regionv in eachof said variable resistance: units .simultaneously,. and a source of intermittent pulsessaid pulse energy source having a value sufficientto reduce the effective valueof said continuous energy source to a value insufficient to produce current-voltage conditions corresponding to said intermediate region: in each of said variable resistance units simultaneously, and a reactive member coupling said connected fixed and variable resistance units.

8. An electrical double-stability circuit coniprising a pair of variable resistance units, a pair offixed'. resistance units connected to respective ones of said variable units, each of said connected fixed and variable units in'combination being characterized by a region of negative resistance within a predetermined range of ourrent-voltage conditions in which operation in either of two stable states is possible, and by first and second regions or positive resistances within adjacent ranges of current-voltage conditions wherein operation in only one stable state is'p0ssib1e," a sourceof continuous unidirectional energy connected across said fixed and variable resistance units, said source being limited in magnitude to a normal value that is less than that required to maintain simultaneously both connected fixed and variable resistance combinations in their second positive resistance region and greater than is required to maintain simultaneously both of said combinations in their first positive-resistance region, means to momentarily reduce the magnitude of said source to a value suflicient only to maintain said connected combinations in their first region of positive resistance, and energy storage means interconnecting said fixed and variable resistance unit combinations.

9. An electrical trigger circuit comprising a pair of variable resistance units, each of which is in series connection with a respective fixed resistance unit, each of said combined fixed and variable units being characterized by a variational resistance characteristic having a predetermined range of current-voltage conditions within which operation in either of two stable states is possible for a given set of conditions and outside of which operation in only one of said stable states is possible for a given set of conditions, a capacitive coupling between the junctions of said fixed and variable units, a source of continuous unidirectional current and a current-limiting resistance in series therewith, said serially connected source and resistance being connected across and interconnecting said fixed and variable resistance units and being of such values that the maximum current flow therefrom equals but does not exceed the current flow sufficient to produce currents within said predetermined range for each of said variable resistance units simultaneously, and a source of unidirectional voltage pulses coupled across each of said fixed resistance units, said pulse source being opposed in polarity to said continuous current source and being of magnitude sufficient to momentarily reduce the current flow from said source to a value less than that sufficient to produce said predetermined range in each of said variable resistance units simultaneously.

10. A double-stability circuit comprising a pair of series-type negative-resistance elements, each of which is paired in series connection with a fixed resistance element, each of said paired resistance elements being characterized by a similar variational resistance characteristic having a predetermined range of current-voltage conditions within which operation occurs in either of two stable states for a given set of conditions and outside of which operation occurs in only one of said stable states for a given set of conditions, a continuous current source connected across and interconnecting said resistance combinations, said source being of such magnitude that the maximum current therefrom corresponds to roughly twice a current value within said predetermined range of current-voltage conditions in one of said negative-resistance elements, a source of unidirectional current pulses the magnitude of which is sufficient to momentarily change the current flow in each of said series-type negative-resistance elements to a value corresponding to current values outside of said predetermined range of current-Voltage conditions, and a capacitive circuit interconnecting the junction points of said series-type negativeresistance elements and said fixed resistance ele- .ments.

11. An electrical trigger circuit comprising a pair of shunt-type negative-resistance units in series connection, a pair of series-connected fixed resistors in parallel connection with said shunttype units, an inductor connected between the junctions of said fixed and shunt-type resistance units, each of said shunt-type units and its parallel-connected fixed resistor being characterized by a variational resistance characteristic that is negative within a predetermined range of current-voltage conditions within which operation occurs in either of two stable states, and outside of which operation occurs in only one of said stable states, and an external network connected across said parallel combination, said network including a source of continuous voltage of a given polarity, a, series-connected source of intermittent voltage pulses, and means to limit the normal current fiow from said continuous voltage source to a value sufficient to produce currents within said predetermined range of currentvoltage conditions in each of said negative-resistance units simultaneously.

12. An electrical trigger circuit comprising a pair of shunt-type negative-resistance units in series connection, a pair of series-connected fixed resistors respectively in parallel combination with each said shunt-type unit, a reactive impedance connected between the junctions of said fixed and said shunt-type resistance units, each of said shunt-type units and its parallel-connected fixed resistor being characterized by a variational resistance characteristic having a predetermined range of current-voltage conditions within which operation occurs in either of two stable states and outside of which operation occurs in only one of said stable states, and an external network connected across said parallel combinations, said network comprising a current-limiting resistor, a source of continuous voltage of a given polarity, and a source of intermittent voltage, said current-limiting resistor being of such value that the maximum current from said continuous voltage source is limited to a current value corresponding to values within said predetermined range of current-voltage conditions in each of said negative resistance units simultaneously.

13. An electrical trigger circuit comprising a pair of similar shunt-type negative-resistance elements in series connection, a pair of seriesconnected fixed resistors connected in parallel with said negative-resistance elements, each of said fixed resistors being of smaller value than the minimum negative resistance of said shunttype elements, an inductor connected between the junction of said shunt-type elements and the junction of said fixed resistors, and an external network connected across said parallel combination, said network comprising a current-limited source of continuous current and a source of intermittent current pulses, said current-limited source being restricted to a value of current equal to roughly twice a value within the range of values at which said shunt-type elements display their negative-resistance characteristics.

14. An electrical trigger circuit comprising a pair of series-connected shunt-type negativeresistance elements, each of said elements having a region of negative resistance over a portion of its current-voltage characteristic, within which operation occurs in either of two stable states for a given set of conditions, a apir of seriesconnected fixed resistors respectively in parallel connection with said shunt-type elements, each of said fixed resistors being of value less than the minimum negative-resistance value of said shunt-type elements, an impedance connection between the junction of said shunt-type elements and the junction of said fixed resistors, a current-limited source of continuous current of a given polarity connected across said parallel combinations, said source being limited to a maximum current value suiiicient to produce the values of current within said negative-resistance portion of said current-voltage characteristics in each of said units simultaneously, and pulse producing means connected to said combination to momentarily reduce the currents through said shunt-type negative-resistance elements to values below those in said negativeresistance portion of their current-voltage characteristic.

15. An electrical trigger circuit comprising a pair of current-conductive paths, each of said paths including a series-type negative-resistance element connected to a fixed resistor, each of said series-type elements having a region of negative resistance for current values within a portion of its current-voltage characteristic within which region operation occurs in either of two stable states in response to a given set of conditions, and having regions of positive resistance for current values outside of said portion within which operation occurs in only one stable state in response to a given set of conditions, each of said fixed resistors being of a value less than the maximum negative reistance of series-type element, an impedance path connected between the junction of said fixed resistor and said series-type element in each currentconductive path, a source of continuous current of given potential connected across and interconnecting said pair of paths, said source being limited to a maximum current equal to the sum of the currents in said current-conductive paths corresponding to said region of negative resistance of said series-type negative-resistance elements, and pulsing means to intermittently change the current in said negative-resistance elements to values outside of those corresponding to said negative-resistance region.

16. An electrical trigger circuit comprising a pair of current-conducting paths, each of said paths including a variable impedance element which is characterized by a variational resist- I ance characteristic having a predetermined range of current-voltage conditions within which operation occurs in either of two stable states, and outside of which operation occurs in only one stable state, a storage circuit connected to intercouple said current-conducting paths, an external network connected across said currentconduction paths, said network including a continuous unidirectional source of energy the magnitude of which is sufiicient to give rise to said predetermined range of current-voltage conditions in each of said current-conducting paths simultaneously, said network also including a source of unidirectional electrical pulses the magnitude of which is sufiicient to momentarily change the current through said current-conducting paths to a value outside said predetermined range of current-voltage conditions.

17. An electrical trigger circuit comprising in combination a pair of variable resistance elements and a pair of connected auxiliary impedance elements forming therewith a pair of current-conduction paths, each of said variable resistance elements in combination with said auxiliary impedance elements having a variational resistance characteristic wherein operation occurs in either of two stable states within a predetermined range of electrical quantities, and wherein operation occurs in only one stable state for electrical quantities outside of said range, an energy storage circuit interconnecting said current-conduction paths, an external network connected across said current-conduction paths, said network including a continuous unidirectional source of energy the magnitude of which is sufficient to give rise to quantities within said predetermined range in each of said ourrent-conducting paths simultaneously, said network also including a source of unidirectional electrical pulses the magnitude of which is sufficient to momentarily change the current through said current-conducting paths to a value outside of said predetermined range.

JOHN G. KREER, JR.

REFERENCES CITED UNITED STATES PATENTS Name Date Eberhard Dec. 5, 1950 Number 

